Method for synchronizing computer clocks in networks used for information transmission, device for carrying out said method and data packet suitable for the synchronization of computer clocks

ABSTRACT

The invention relates to a method for synchronizing computer clocks in networks used for the transmission of information according to which information is dispatched with a time stamp when being dispatched and which is re-transmitted with a time stamp in a confirmation of receipt. The time stamps are inserted in the outgoing or arriving data packet by a clock module ( 8 ) mounted downstream of a network controller ( 4, 10 ) once said network controller has authorized transmission. A CPU ( 2 ) generates actuator signals that are provided with an identifier and that correct the clock modules ( 8 ) on the basis of a comparison between the time stamps in a confirmation of receipt of the addressee of the information and the time stamp of the corresponding transmitted information.

[0001] The invention relates to a method for synchronizing computer clocks in networks for the information transfer, in which information is sent with a time stamp at the moment of its sending, and is returned with a time stamp in a receipt confirmation, a device for synchronizing computer clocks in networks for the information transfer, in which the information is equipped with a time stamp at the moment of its sending, and with a time stamp at the moment of receipt at the target address, as well as a data packet for synchronizing computer clocks in information transfer networks for networked computers.

[0002] In addition to a central processing unit (CPU) and a memory, a computer also requires interfaces to the outside for its operation that can be constructed in different ways. A system bus is directly connected to the computer, which is generally constructed as a parallel interface so that depending on the processor clock, or on the bus clock, a multitude of bits can be allowed in and out. If information is to be transferred via lines, this can generally also occur via parallel interfaces, whereby the line length is limited due to the large amount of lines required. Transfer processes were therefore developed for the distance transfer of information or data, in which the initially parallel existing signals were converted into serial signal so that they could be sent and received in a succession via a low amount of lines. For this purpose, computers are usually equipped with network cards that are connected to the respective system bus, whereby standard parallel interfaces were recommended in this case.

[0003] One example of such a standard interface is the so-called PCI bus. A network controller or a network card is successively connected to such a bus, which in addition to the network controller also contains an additional interface that is adjusted to the selected transfer medium, or to the selected network structure. Among other tasks, this media-specific interface takes on the adjustment of the levels to the post-connected line network, whereby bus networks are commonly used. In the case of bus networks, all computers are connected to a mutual bus, whereby each participant can access the bus, and can reach each participant connected. In order to control access to such bus structures, the CSMA (carrier sense multiple access) process is used, for example. In this process, an attempt is made to avoid collisions by simultaneously occurring transfers. If two participants simultaneously recognized and sent a free line network, such collisions would occur. However, this is prevented by the fact that the transfer media is tapped by the stations before the transfer is started, for which bit structures are used with which collision recognition is possible. Such bit structures are called CSMA/CD packets, whereby CD stands for “collision detection” or collision recognition. In addition to bus networks, star networks, ring networks, and token ring networks are common, and various types of transfer protocols are used with which a more or less large maximum transfer speed can be achieved. Such transfer protocols have been known, for instance, as Ethernet protocols (IEEE803), or as firewire protocols (IEEE1394). The analog applies to, for instance, CAN, FDDI, ATM, or gigabit Ethernet protocols.

[0004] The network controller, together with the media-specific interface, provides the translation of the parallel data flows into a serial data flow, whereby the desired conventions, or protocols are maintained in order to avoid any collisions. Network cards usually contain memory in order to retain information as long as a data line is occupied, or the data packet is incomplete, or is present in a form that is unsuitable for the protocol. This stored information is subsequently fed into the network when a free line is detected. Because of this intermediate storage until the release of transfer, the data packets experience various delays due to the network card. This is also true for so-called switches, in which certain information is stored up until a certain time for an addressee, to which a larger packet can be sent at a higher speed.

[0005] In computer networks that must be checked to ensure that a universal time base is available to all computers, it is also important to recognize when the information was received from another networked computer in addition to when the information was sent. Although computer clocks for the clocking of a computer allow for the determination of time at which a processor has made information available to the network card, they do not recognize when the network card has actually performed the transfer via the data transfer line. Therefore, additional computer clocks have been recommended, by means of which the time critical data packets are equipped with a time stamp at the time of the actual transfer. Such computer clocks have already been connected between the network controller and the media-specific interface, whereby the network controller and the media-specific interface are connected to each other via a media-independent interface (MIIF), and the computer clock is connected between these two components. In order to make complete information on the actual time of transfer of the information available to the respective sending CPU, this inter-connected computer clock must echo the time of the actual transfer to the assigned processor. In this regard, it is advisable to perform an echo into the system bus via a separate component group, whereby such components can be called PCI bridges, for instance, and communicate with the PCI bus of the computer. The connection-technical and hardware expenditure of such modifications, however, is relatively high and requires the additional equipment of computers with additional interfaces and additional interface cards,

[0006] The invention is aimed at reducing the hardware and connection-technical expenditure for the synchronization of a universal time base in information transfer networks, and to avoid hardware changes after the fact so that the desired universal time base can be achieved at a substantially higher precision by merely performing a respective software adjustment. In solving this task the inventive method essentially consists of the fact that the time stamps are inserted by a post-connected clock module into the outgoing or incoming data packet after the release of the transfer by a network controller, and that a CPU generates positional signals for the correction of the clock module that are equipped with identification from the comparison of time stamps in a receipt confirmation by the addressee of the information and the time stamp of the relating information sent. By the fact that the time stamps are inserted after release of the transfer by means of network switching by a clock module, such clock modules can be arranged within the media-independent interface, and can also be arranged directly on the network card so that merely the respective network card must be connected to the respective system bus of the processor. At the same time, this arrangement ensures that the time stamp is not actually inserted until the network controller performs the transfer. However, an echo of the correct receipt, which is simultaneously equipped with a time stamp, does not necessarily lead to a respectively active synchronization of the clock circuit as the positional signals, or the setup signals, as well as possibly the control signals and/or the status signals must be exchanged with the clock module for purposes of improving the precision and accuracy of the time basis. However, such positional signals may be sent only by the assigned CPU or a special network processor, when an error of the time basis due to exterior influences is to be safely avoided, whereby these control signals may be processed only by the respectively responding clock module. In the controlling of all clocks by a single processor in the network, the data transfer of each clock to the control processor is achieved by means of a simple (undocumented) return transfer of the data packet by each local CPU. The required echo of status information by echoing all data packets identified for the local computer clock to the other computer can occur by the local CPU for the purpose of correction and control of a local computer clock by means of another computer in the network. According to the invention, a CPU generates positioning signals that are equipped with identification from the comparison of the time stamp contained in a receipt confirmation of the addressee of the information and the time stamp of the information it has sent, and provides this exclusively to the clock module, which is to perform the respective correction. Therefore, the identification additionally required in the course of such positioning signals ensures that the clock module assigned to a computer can selectively respond, and in itself cannot be influenced by any signals from the network so that a high degree of safety, as well as a higher precision provided by the possibility of a continuous or iterative reset can be achieved.

[0007] Advantageously, the inventive method is performed in such a way that positioning signals for the correction, control signals and/or status signals of the clock modules are transferred with identification that is evaluated by a packet detection logic of a clock module, and that such positioning signals transferred with identification are used for the correction of the time of the respective clock module. Principally, as previously mentioned, a separate bus connection for the echo to the related CPU should be avoided for reasons of simplifying the expenditure of hardware. In order to ensure that the respective positioning signals, control signals and/or status signals are actually transferred only to the respectively assigned clock module, it is therefore necessary to ensure that the identifications are detected and evaluated by a component of the clock module itself, or the network controller.

[0008] Some media-specific interfaces, for instance, can be switched by means of an additional data line in such a way that such signals are transferred back not to the network, but to the CPU, which have generated the signals, whereby such an interface switching can also be realized directly in a component group that contains the clock circuit. Advantageously, the action chosen for this purpose is that the network controller communicates directly with an interface circuit and generates a command for the return of positioning, control, and/or status signals that are sent to the clock circuit by a CPU to the CPU that has generated the signals.

[0009] In this regard it is principally possible and of benefit to use a special processor for the synchronization, whereby the action advantageously chosen for this purpose is that the data packets for the correction, control, and status signals of a local computer clock are calculated on another computer in the network, and are sent out as a data packet to the network controller of the respective computer clock.

[0010] In an especially simple manner, the synchronization of computer clocks in networks occurs by means of switches, whereby the residence time of each data packet is measured in a switch for a local computer clock together with correction, control, and status signals, and each switch is equipped with a computer clock and suitable time measurement device at all switch ports.

[0011] The inventive device for synchronizing a universal time basis is essentially characterized that a clock module is assigned to each network controller, which contains a packet detection logic and a clock controller, whereby positioning, control, and/or status signals sent out by a CPU are performed, or processed after the clock controller checks the target address in the network controller, and information is entered into the detected packet. As previously mentioned, the detection of the signals equipped with identification can be performed by a component of the clock module. The device can also be embodied in such a way that the network controller is connected to the interface via a separate line for the transmission device reverse, bypassing the clock module, in order to detect positioning, control, and/or status query signals.

[0012] In order to additionally reduce the extent of switching-technical modifications, however, such a separate control line between the network controller and the media-specific interface can be omitted if the respective logic for the detection of positioning, control, and/or status query signals and a respective interface are integrated into the clock module that is switched to the media-independent interface, which performs the return of such signals to the respective CPU that has generated the signals. Advantageously, the embodiment is therefore chosen so that the packet detection lock for the detection of positioning, control, and/or status query signals, and the related computer clock are combined into one component group, and particularly are integrated. This creates a particularly simple circuit arrangement that can be easily integrated into conventional network card, in which it is subsequently merely necessary to provide the CPU with the possibility by means of respective software programming, to evaluate the returning signals correspondingly in order to generate the required setup signals for the post adjustment of the clock module.

[0013] The inventive data packet for the synchronization of clock circuits in information transfer networks for networked computers is for this purpose characterized that the data packet contains at least one identification for packet types in addition to the fields for the target address, source address, and data, which is characteristic for positioning, control, and/or status query signals. The common transfer protocols, as they are applied in data and communication technology, usually contain a defined amount of bits for the packet type detection so that such identifications can be accommodated without modification, for instance in the bit structure of CSMA data packets with collision identification.

[0014] The invention is explained in further detail by the embodiment examples schematically illustrated in the drawing as follows.

[0015] It shows in FIG. 1 an initial embodiment of the inventive device in the form of a block circuit diagram,

[0016] and in FIG. 2 a further embodiment of the inventive device.

[0017]FIG. 1 shows a clock identified by 1 for a CPU 2. The CPU 2 hereby represents the central component of the processor that is connected to a network controller 4 of a network card via a bus structure 3 embodied as a parallel bus. In the illustration according to FIGS. 1 and 2, a bus structure was selected as an example, the backbone of which is identified by 5. The connection to this backbone of the network is created by means of the media-specific interface 6, in which the adjustment to the levels required by the respective medium also occurs. Lines 7 are provided between the media-specific interface, or the interface 6 and the network controller 4, which all represent a media-independent interface between the network controller 4 and the media-specific interface 6. A clock module 8 is switched into these lines 7 that equips the media packet with a time stamp in case of time-critical information every time when the network controller relays a data packet to the media-specific interface 6. The echo that a signal has been received by another CPU 2 occurs via the line 5, the media-specific interface 6, the network controller 4, and the parallel bus 3 to the CPU 2. A comparison of the time stamp of the sending CPU's clock module with the time stamp of the receiver permits a conclusion as to the accuracy of the time basis in consideration of the known or measured run time of the signals between two known addresses, and subsequently enables a CPU 2 to generate signals with which the clock frequency of the own clock module 8 is adjusted accordingly in order to increase accuracy. Synchronizations can be achieved in this way in which the known maximum deviation of the clocks in the clock generators of processors that are different from each other can be maintained within a nanosecond range. The respective setup or positioning signals are now relayed from a CPU 2 to the clock module 8 via the network controller 4, whereby according to the embodiment shown in FIG. 1, the network controller 4 itself is capable of detecting such setup signals due to their identification as setup signals. In these cases, the network controller 4 communicates to the media-specific interface 6 via the line 9 that this information is not intended for a relay to the network 5, but instead is to be returned to its own CPU 2 together with a respective confirmation by the clock module 8 of the correction performed.

[0018] The embodiment according to FIG. 2 essentially uses the same components, whereby the additional control line 9 is omitted. In this embodiment, the clock module 8 by which the time stamp is applied, contains an additional simple variation of a network controller 10 in the form of a packet detection logic and a clock controller 11 so that the respective detection of setup signals can occur within the component group contained in the clock module 8. 

1. Method for the synchronizing of computer clocks in networks for the information transfer, in which information is sent with a time stamp at the moment of its sending, and is returned with a time stamp in a receipt confirmation, characterized that the time stamps are inserted by a post-connected clock module (8) into the outgoing or incoming data packet after the release of the transfer by a network controller (4, 10), and that a CPU (2) generates positional signals for the correction of the clock modules (4) that are equipped with identification from the comparison of time stamps in a receipt confirmation by the addressee of the information and the time stamp of the relating information sent in consideration of the known or measured run times of the signals between the sender and the addressee.
 2. Method according to claim 1, characterized that positioning signals for the correction, control signals and/or status signals of the clock modules (8) are transferred with identification that is evaluated by a packet detection logic of a clock module (8), and that such positioning signals transferred with identification are used for the correction of the time of the respective clock module (8).
 3. Method according to claims 1 or 2, characterized that the network controller (4) with an interface circuit (6) and generates a command for the return of positioning, control, and/or status signals that are sent to the clock module (8) by a CPU (2) to the CPU (2).
 4. Method according to claims 1, 2, or 3, characterized that the data packets for the correction, control, and status signals of a local computer clock (8) are calculated on another computer in the network, and are sent out as a data packet to the network controller (4, 10) of the respective computer clock (8).
 5. Method according to one of the claims 1 to 4, characterized that the synchronization of computer clocks (8) in networks occurs by means of switches, whereby the residence time of each data packet is measured in a switch for a local computer clock (8) together with correction, control, and status signals, and each switch is equipped with a computer clock (8) and suitable time measurement device at all switch ports.
 6. Device for synchronizing computer clocks in networks for the information transfer, in which the information is equipped with a time stamp at the moment of its sending, and with a time stamp at the moment of receipt at the target address, characterized that a clock module (8) is assigned to each network controller (4, 10), which contains a packet detection logic and a clock controller (11), whereby positioning, control, and/or status signals sent out by a CPU (2) are performed, or processed after the clock controller (11) checks the target address in the network controller (4, 10), and information is entered into the detected packet.
 7. Device according to claim 6, characterized that the packet detection lock for the detection of positioning, control, and/or status query signals, and the related computer clock (8) are combined into one component group, and particularly are integrated.
 8. Data packet for the synchronization of clock circuits in information transfer networks for networked computers, characterized that the data packet contains at least one identification for packet types in addition to the fields for the target address, source address, and data, which is characteristic for positioning, control, and/or status query signals. 